Embodiments of the invention are directed, in general, to communication systems and, more specifically, to the multiplexing of uplink reference signals and the partitioning of scheduling bandwidths in communication systems.
Embodiments of the invention apply, inter alia, to DFT-spread OFDMA frequency division multiple access (FDMA) communication systems, also commonly referred to as single carrier FDMA or SC-FDMA, such as the one adopted in EUTRA. The EUTRA sub-frame structure 100 is shown in FIG. 1 and consists of long blocks (LB) 110 and short blocks (SB) 121 & 122, where each block has a corresponding cyclic prefix (CP) 130. Cyclic Prefix (CP) durations are not necessarily the same for all blocks. Uplink pilot (also referred to as reference signal) transmission is assumed to be confined in SB1 121 and SB2 122 whereas the data and/or control transmission occupies long blocks (LBs). Unless explicitly mentioned otherwise, data transmission refers to either data or control transmission. The use of SB for data or partial use of a LB for RS can be optional, and is not precluded.
FIG. 2 is a block diagram showing a DFT-spread OFDM(A) transmitter, with “localized” sub-carrier mapping; thus, FIG. 2 is also an example of “localized” SC-OFDM(A) transmitter. It comprises of Modulated Symbols 201, serial to parallel conversion 202, Discrete Fourier Transform (DFT) block 203, Inverse Fast Fourier Transform (IFFT) block 206 Parallel to Serial (P/S) converter 207, and RF block 208. Zero padding is inserted in sub-carriers 205 (used by another UE) and 204 (guard sub-carriers), cyclic prefix is added at 210. Elements of apparatus may be implemented in hardware or as components in a programmable processor or Digital Signal Processor (DSP).
FIG. 3 is a block diagram showing a DFT-spread OFDM(A) (bracketed letter “A” means that the statement holds for both DFT-spread OFDM and DFT-spread OFDMA) transmitter, with “distributed” sub-carrier mapping; thus, FIG. 3 is also an example of “distributed” SC-OFDMA transmitter. It comprises of Modulated Symbols 301, serial to parallel conversion 302, Discrete Fourier Transform (DFT) block 303, Inverse Fast Fourier Transform (IFFT) block 306 Parallel to Serial (P/S) converter 307, and RF block 308. Zero padding is inserted in sub-carriers 305 (used by another UE) and 304 (other zero sub-carriers, which can be used by other UEs or as guard sub-carriers), cyclic prefix is added at 310. Elements of apparatus may be implemented in hardware or as components in a programmable processor or Digital Signal Processor (DSP).
Either localized (FIG. 2) or distributed (FIG. 3) DFT-spread OFDMA may be applied to either one of short blocks (SB) or long blocks (LB). FIGS. 2 and 3 only convey the spirit of the transmission, and not the exact numerology as the DFT size may typically consist of tens or hundreds of sub-carriers.
For localized DFT-spread OFDMA transmission, the set of used (by an individual UE) sub-carriers is contiguous, whereas for distributed DFT-spread OFDMA transmission, the set of used (by an individual UE) sub-carriers is non-contiguous and the sub-carriers are equally spaced. This is illustrated in FIG. 4, moreover, because in the exemplary embodiment of the EUTRA uplink sub-frame structure in FIG. 1, the SB duration is half the LB duration, the sub-carrier bandwidth in SB (both in SB1 and SB2) is twice as large as the one in LB. Obviously, for a different relative duration of SB and LB, the corresponding sub-carrier spacing will scale proportionally. The set of LB sub-carriers is divided into resource blocks (RBs) for purposes of multiple access and channel dependent (frequency and/or time domain) scheduling. For localized LB data transmission, a RB contains an integer number of contiguous sub-carriers. The operating system bandwidth is divided into multiple LB RBs whose number N is (typically, but not necessarily) given by the ratio of the operating system bandwidth over the RB size. The scheduler may assign one or more (typically consecutive) RBs to a particular UE and scheduling granularity is one or more sub-frames.